Known self-watering systems for plants grown in pots do not encourage optimum root development in the plants. Baumgartner et al., U.S. Pat. No. 4,819,375, describes a receptacle for plants having a water-permeable membrane forming the base of the pot. Water enters the plant pot through the membrane, from a reservoir surrounding the pot. In use, the device of Baumgartner et al. is filled with water to a depth depending on the desired wetness of the growing medium.
Biancardi, U.S. Pat. No. 4,315,599, describes an apparatus which is supported outside the plant container. The soil dryness in the root area is measured using an electrically operated probe in the root area. A thermocouple connected to the probe controls a condensation system which allows water to drip onto the soil.
The patent to Crane, Jr., U.S. Pat. No. 3,758,987, describes a system in which water enters the pot through a permeable membrane in the base of the pot. The water is stored in a reservoir surrounding the sides of the pot and is allowed to seep into the soil when air contained in the soil indicates soil dryness.
Benesch, U.S. Pat. No. 3,512,712, describes an automatic watering device in which soil dryness is indicated by expansion and contraction of a series of wooden blocks linked to an electric switch which controls the water supply valve. Water is allowed to flow when the wooden blocks are in a contracted state.